JP2009298102A - Laser-engravable flexographic printing original plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser-engravalbe printing original plate which can produce a forme which prevents the occurrence of defective printing and is excellent in resolution. <P>SOLUTION: A photosensitive resin composition containing at least latex having an average degree of gelation of at least 20% (A), a photopolymerizable compound (B), and a photopolymerization initiator (C) is irradiated with light, crosslinked, and cured to obtain the printing original plate. In the laser-engravable flexographic printing original plate, the photopolymerizable compound (B) contains a polyfunctional monomer having a molecular weight of 1,000 or below and three ethylenic unsaturated groups in a molecule and monofunctional monomer having one ethylenic unsaturated group in a molecule. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a laser-engravable flexographic printing plate for producing a printing plate that does not cause printing defects and has excellent resolution.

  A flexographic printing plate is a plate making method (negative method) in which an original film is placed on a photosensitive resin layer, the exposed resin is crosslinked by exposure, and then the uncrosslinked resin in the unexposed area is washed away with a developer. Until now. However, recently, a method (CTP method) is becoming popular in which information processed on a computer is directly output on a printing plate to obtain a relief uneven pattern. Among them, laser engraving that performs engraving with a laser does not require an original film and does not require a development process, so is an extremely efficient and environmentally friendly method (see Patent Document 1). Consideration has been made.

  In the printing plate manufacturing process by laser engraving, unevenness is formed on the plate surface by irradiating the printing original plate with a laser beam based on the image data to decompose and remove the irradiated portion. At this time, resin debris is generated due to the decomposition of the image forming material in the laser irradiation portion, and a part thereof is scattered over the entire printing plate. Since these resin wastes cause problems when left on the printing plate, they are removed from the printing plate by sucking with a dust collector provided near the laser device during laser irradiation and / or by washing the printing plate after laser irradiation. Removed.

  However, since the printing original plate is mainly composed of synthetic rubber, the original plate itself has high adhesiveness, and the resin residue generated by laser irradiation adheres to the plate without being removed even by suction during laser irradiation or washing after laser irradiation. It has a problem that it is easy to remain. If the resin residue remains attached to the laser non-irradiated portion (convex portion) of the printing plate, this portion is a portion to which ink is applied at the time of printing, leading to printing defects. In addition, if the resin residue remains attached to the bottom of the laser-irradiated portion (recessed portion) of the printing plate, the depth of the halftone dot is reduced. In either case, the resolution may be lowered.

  As a method for overcoming the disadvantages of the above materials, a technique for improving the mechanical properties of the printing original plate by blending a resin composition with a colorless and transparent filler such as silica fine powder, resulting in a decrease in adhesiveness has been proposed. (See Patent Document 2). However, the method of blending a filler such as silica fine powder requires a large amount of filler in order to sufficiently reduce the adhesiveness of the printing original plate, and there is a problem that the moldability and physical properties of the printing original plate are remarkably impaired. there were. Thus, since the addition of the filler adversely affects the moldability and physical properties of the printing original plate, development of a method capable of reducing the adhesiveness of the printing original plate without adding the filler has been demanded. .

As a method therefor, the present inventors have already proposed a method capable of producing a flexographic printing plate having no resolution and excellent resolution by using latex as the main component of the photosensitive resin composition ( (See Patent Document 3). In the patent, a printing plate with less engraving residue is proposed by containing a hydrophobic polymer and a photopolymerizable oligomer obtained from at least two kinds of water-dispersed latex, and an image forming property of 150 lpi is achieved.
Special table 07-506780 Special table 2004-533343 JP 2006-100168 A

  Recently, however, printed materials have been required to be more delicate and even in flexographic printing, higher printing performance has been required from 150 lpi to 175 lpi. However, in Patent Document 3, fine dot reproducibility of 1 to 3% of fine 175 lpi is insufficient, and a master plate for laser engraving excellent in image reproducibility has been demanded.

  The present invention was devised in view of the current state of the prior art, and its purpose is to produce a printing plate capable of laser engraving capable of producing a printing plate that does not cause printing defects due to resin residue and has excellent resolution. Is to provide.

  As a result of intensive investigations to achieve such an object, the present inventors have not used a photopolymerizable oligomer in which the photopolymerizable compound has the same skeleton structure as the latex component as a component of the printing original plate as a component of the printing original plate, Photosensitive resin layer comprising a combination of a polyfunctional monomer having three or more ethylenically unsaturated groups in one molecule having a molecular weight of 1,000 or less and a monofunctional monomer having one ethylenically unsaturated group in one molecule It has been found that by using a printing original plate made of the above, it is possible to reduce the generation of resin residue caused by laser irradiation and adhesion to the printing plate, and to overcome these problems, and have completed the present invention.

  The laser-engravable printing original plate of the present invention does not use a photopolymerizable oligomer in which a photopolymerizable compound contains the same skeleton structure as the latex component as a component of the printing original plate. The polyfunctional monomer having the above ethylenically unsaturated group and a monofunctional monomer having one ethylenically unsaturated group in one molecule are included. Since it does not contain a photopolymerizable oligomer having a molecular weight exceeding 1,000, adhesion and fusion of engraving residue to the plate caused by laser irradiation during the production of the printing plate can be suppressed very little. If the printing original plate obtained from the present invention is used, it is possible to provide a printing plate with less adhesion of resin residue, and to produce a printing plate that does not cause printing defects caused by these and has excellent resolution. be able to.

  The printing original plate of the present invention comprises (1) a photosensitive resin composition containing at least (A) a latex having an average degree of gelation of 20% or more, (B) a photopolymerizable compound, and (C) a photopolymerization initiator. Is a printing original plate obtained by light-irradiating and curing by crosslinking, wherein (B) a polyfunctional monomer having three ethylenically unsaturated groups in one molecule having a molecular weight of 1,000 or less and 1 A laser-engraveable flexographic printing plate comprising a monofunctional monomer having one ethylenically unsaturated group in a molecule. (2) The flexographic printing plate capable of laser engraving according to claim 1, wherein the molecular weight of the other functional monomer in (B) the photopolymerizable compound is 500 or less. (3) (B) The polyfunctional monomer of the photopolymerizable compound is one or more compounds selected from trimethylolpropane triacrylate, trimethylolpropane trimetaacrylate, or pentaerythritol triacrylate, and the monofunctional monomer is lauryl. 3. The laser-engravable flexographic printing original plate according to claim 1 or 2, which is methacrylate or stearyl (meth) acrylate.

  The present inventors have compared the component (A) with a polyfunctional monomer having three ethylenically unsaturated groups in one molecule having a molecular weight of 1,000 or less as component (B) and one ethylenic in one molecule. By using a monofunctional monomer having an unsaturated group, it is possible to lead to a crosslinked state (mesh) suitable for laser engraving properties, printing without causing defective printing due to adhesion of resin residue, and excellent resolution. We found that plates could be produced.

In the present invention, as the component (B), the molecular weight of the polyfunctional monomer having three ethylenically unsaturated groups in one molecule is 1000 or less, preferably 500 or less.
As the component (B), when the molecular weight of the polyfunctional monomer exceeds 1000, the entanglement due to the network structure of the latex component is insufficient, so that the laser engraving property is inferior.

(B) component used for this invention is 25 mass% or more and 50 mass% or less in all the compositions, Preferably it is 25 mass% or more and 45 mass% or less, More preferably, it is 30 mass% or more and 45 mass% or less. When the content of the component (B) is less than 25% by mass relative to the total composition, the amount is insufficient as a crosslinking component for forming a network, and when it exceeds 50% by mass, the composition is formed into a sheet. The handleability is very poor due to insufficient hardness after molding.
On the other hand, the ratio of the polyfunctional monomer having three or more ethylenically unsaturated groups in one molecule having a molecular weight of 1,000 or less used for the component (B) and the monofunctional monomer is 90/10 to 50/50 (mass% / Mass%), preferably 85/15 to 50/50 (mass% / mass%), more preferably 80/20 to 60/40 (mass% / mass%). When the monofunctional monomer is less than 10% by mass, the laser engraving property is excellent, but since the printing plate is inferior to the printing durability and the solid ink, it does not satisfy both the laser engraving property and the printing property. . On the other hand, when the monofunctional monomer exceeds 50% by mass, the printing plate is excellent in printing durability and solid ink, but the laser engraving property is inferior, so that both the laser engraving property and the printing property are satisfied. I can't get it.

The photo-curing of the present invention is a synthetic rubber-based photosensitive resin composition formed into a sheet shape, and the sheet-shaped molded product is exposed to an ultraviolet light exposure machine (light source: manufactured by Philips Co., Ltd.) at a distance of 5 cm from the surface to 8 mW / cm ² . 10R), the front and back surfaces are exposed for 10 minutes to be crosslinked and cured.

The (A) latex constituting the resin composition of the present invention is a main component of the image forming material, and has a role of forming a concave portion by being decomposed by laser irradiation according to the image on the printing original plate. The present invention is characterized in that a latex having a gelation level of a certain level or more is used as the latex. When a non-gelled latex is used, the adhesiveness increases when processed into a printing original plate even if the adhesiveness is low in the state of the resin composition. This is because latex fine particles are fused or aggregated by heating or pressurizing when a resin composition is molded into a printing original plate or by addition of a solvent, and no longer exist in the state of fine particles by agglomeration or integration. Because it ends up. Therefore, in order to prevent aggregation and integration of latex fine particles during molding into a printing original plate and maintain low adhesion even in the printing original plate, use a gelled hard crosslinked latex. is required. Rubber latex refers to an emulsion in which a polymer such as natural rubber, synthetic rubber or plastic is colloidally dispersed in water by the action of an emulsifier. Natural rubber latex as a product, (ii) synthetic rubber latex synthesized by emulsion polymerization, and (iii) artificial latex in which solid rubber is emulsified and dispersed in water, are used in the present invention (A). Latex refers only to the above (ii) synthetic rubber latex and (iii) artificial latex, and does not include (i) natural rubber latex.
The latex used in the present invention is preferably ii) a synthetic rubber latex synthesized by an emulsion polymerization method.

The gelation degree of the latex (A) used in the present invention needs to be 20% or more on average. (A) The degree of gelation of the latex is preferably 45% or more, and more preferably 65% or more. The degree of gelation is the weight average degree of gelation, and it is possible to satisfy the degree of gelation with a single latex. However, the desired average degree of gelation can be achieved by mixing with a latex having a degree of gelation of 0% or a different degree of gelation. Degree can be achieved.
When the gelation degree of the latex is less than the above value, aggregation and integration of latex fine particles during molding on the printing original plate cannot be sufficiently prevented, and the adhesiveness of the printing original plate may not be maintained low. On the other hand, there is no limit to the upper limit of the gelation degree of latex, and the larger the gelation degree, the better the aggregation and integration preventing effect of latex particles. In addition, the value of the gelation degree of latex is prescribed | regulated by the insolubility in toluene. Specifically, the gelation degree of the latex was measured by accurately weighing 3 g of the latex solution on a 100 μm thick PET film, dried at 100 ° C. for 1 hour, and then immersed in a toluene solution at 25 ° C. for 48 hours. It is measured by drying at 110 ° C. for 2 hours and calculating the weight percentage of insoluble matter.

  The latex (A) used in the present invention may be appropriately selected from conventionally known latexes having a certain degree of gelation degree. Specific examples include polybutadiene latex and styrene-butadiene copolymer. Polymer latex, acrylonitrile-butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex, polyisoprene latex, etc. are mentioned, among them polybutadiene latex, acrylonitrile-butadiene copolymer latex, methyl methacrylate-butadiene copolymer. Latex is preferred. These latexes may be modified with (meth) acrylic or carboxy as desired. In addition, since many various synthetic | combination or natural latex is marketed as the gelatinized latex, what is necessary is just to select an appropriate thing from there. Moreover, latex may be used independently or may use 2 or more types together. When two or more kinds of latexes are used, the gelation degree indicates the weight average of these.

  The photopolymerizable compound used in the present invention is a compound that can be cross-linked by ultraviolet rays, and is a monomer having one and three ethylenically unsaturated groups in the molecule.

As the component (B), the ethylenically unsaturated monomer having three or more ethylenically unsaturated bonds used in the present invention includes trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra ( Trimethylolpropane obtained by the addition reaction of a compound having an ethylenically unsaturated bond such as unsaturated carboxylic acid or unsaturated alcohol and active hydrogen to triglycidyl ether of meth) acrylate, glycerol tri (meth) acrylate or polyhydric alcohol And triglycidyl ether tri (meth) acrylate. Among these, trimethylolpropane tri (meth) acrylate and pentaerythritol tri (meth) acrylate are preferable.
On the other hand, as a compound having one ethylenically unsaturated bond used in the present invention, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isoamyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, alkyl (meth) acrylate such as stearyl (meth) acrylate, cycloalkyl (meth) acrylate such as cyclohexyl (meth) acrylate, chloroethyl (meth) acrylate, chloropropyl ( Alkoxyalkyl such as alkyl (meth) acrylate such as meth) acrylate, methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate Phenoxyalkyl (meth) acrylates such as (meth) acrylate, phenoxyethyl acrylate, nonylphenoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxytriethylene glycol (meth) acrylate, methoxydipropylene glycol (meth) acrylate, etc. Alkoxyalkylene glycol (meth) acrylate, and the like. Of these, alkyl (meth) acrylate is preferable, and lauryl (meth) acrylate and stearyl (meth) acrylate are particularly preferable.

  The photopolymerization initiator (C) of the present invention has a role as a catalyst for the photopolymerization / crosslinking reaction of the photopolymerizable compound (B). As the photopolymerization initiator (C) used in the present invention, any photopolymerization initiator can be used as long as it can polymerize a polymerizable carbon-carbon unsaturated group by light irradiation. Those having a function of generating radicals by autolysis or hydrogen abstraction are preferably used. Specifically, for example, benzoin alkyl ethers, benzophenones, anthraquinones, benzyls, acetophenones, diacetyls and the like can be used.

  In the resin composition of the present invention, optional components such as a hydrophilic polymer, a plasticizer, and / or a polymerization inhibitor can be blended as desired in addition to the above-mentioned three components (A) to (C).

  The hydrophilic polymer has an effect of improving the printing property by improving the affinity between the printing plate and the water-based ink when the flexographic printing is performed using the produced printing plate. The hydrophilic polymer that can be used in the resin composition of the present invention is -COOH, -COOM (M is a monovalent, divalent, or trivalent metal ion or a substituted or unsubstituted ammonium ion), -OH , —NH 2, —SO 3 H, and those having a hydrophilic group such as a phosphate ester group are preferred. Specifically, a polymer of (meth) acrylic acid or a salt thereof, (meth) acrylic acid or a salt thereof and an alkyl (meta ) A copolymer of acrylate, a copolymer of (meth) acrylic acid or a salt thereof and styrene, a copolymer of (meth) acrylic acid or a salt thereof and vinyl acetate, a (meth) acrylic acid or a salt thereof Copolymer with acrylonitrile, polyvinyl alcohol, carboxymethyl cellulose, polyacrylamide, hydroxyethyl cellulose, polyethylene Side, polyethyleneimine, polyurethane having -COOM group, polyureaurethane having -COOM group, include the polyamic acid and their salts or derivatives having a -COOM group. These may be used alone or in combination of two or more. The blending ratio of the hydrophilic polymer in the resin composition of the present invention is preferably 20% by mass or less, and more preferably 15% by mass or less. When the blending ratio of the hydrophilic polymer exceeds the above upper limit, the water resistance of the printing plate to be produced is lowered, and the water-based ink resistance may be lowered.

  The plasticizer has an effect of improving the fluidity of the resin composition and an effect of adjusting the hardness of the printing original plate to be produced. The plasticizer that can be used in the resin composition of the present invention preferably has good compatibility with the synthetic rubber (A), and more preferably is a polyene compound that is liquid at room temperature. Examples of the polyene compound that is liquid at room temperature include liquid polybutadiene, polyisoprene, and maleated products and epoxidized products having their end groups or side chains modified. The blending ratio of the plasticizer in the resin composition of the present invention is preferably 20% by mass or less, and more preferably 10% by mass or less. When the blending ratio of the plasticizer exceeds the above upper limit, the mechanical properties and solvent resistance of the printing plate are remarkably lowered, and the printing durability may be lowered.

  The polymerization inhibitor has an effect of increasing the thermal stability of the resin composition. The polymerization inhibitor that can be used in the resin composition of the present invention may be a conventionally known one, and examples thereof include phenols, hydroquinones, and catechols. The blending ratio of the polymerization inhibitor in the resin composition of the present invention is preferably 0.001 to 3% by mass, and more preferably 0.001 to 2% by mass.

  Further, as optional components other than these, a colorant, an antioxidant and the like can be added within a range not impairing the effects of the present invention.

  The resin composition of the present invention is prepared by mixing the above-described three essential components (A) to (C) and optionally an optional component. At that time, an organic solvent such as toluene may be added as desired to facilitate mixing. Further, in order to complete the mixing, it is desirable to sufficiently knead under a heating condition using a kneader. It is preferable that heating conditions are about 50-110 degreeC. Moreover, it is preferable that the organic solvent added at the time of mixing and the water contained in the components are removed under reduced pressure after kneading.

  Next, the printing original plate capable of laser engraving of the present invention will be described. The printing original plate of the present invention is obtained by molding the resin composition of the present invention prepared as described above into a sheet or cylinder, and then irradiating the molded product with light to crosslink and cure. is there.

  As a method for molding the resin composition of the present invention into a sheet or cylinder, a conventionally known resin molding method can be used. For example, the resin composition of the present invention can be used on a suitable support or in a printing machine. The method of apply | coating on a cylinder and pressurizing with a heat press machine etc. can be mentioned. As the support, a material having flexibility and excellent dimensional stability is preferably used, and examples thereof include polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, and polycarbonate. The thickness of the support is from 50 to 250 μm, preferably from 100 to 200 μm, from the viewpoints of mechanical properties and shape stability of the printing original plate. Further, if necessary, a known adhesive conventionally used for this type of purpose may be provided on the surface in order to improve the adhesion between the support and the resin layer. The pressurization condition is preferably about 20 to 200 kg / cm 2, and the temperature condition during pressurization is preferably about room temperature to about 150 ° C. The thickness of the formed product may be appropriately determined depending on the size and properties of the printing original plate to be produced, and is not particularly limited, but is usually about 0.1 to 10 mm.

  Next, the molded resin composition is irradiated with light to polymerize and crosslink the (B) photopolymerizable compound in the resin composition, thereby curing the molded product to obtain a printing original plate. Examples of the light source used for curing include a high-pressure mercury lamp, an ultra-high pressure mercury lamp, an ultraviolet fluorescent lamp, a carbon arc lamp, and a xenon lamp, and the curing can be performed by other known methods. Although the light source used for curing may be one type, the curability of the resin may be improved by curing using two or more types of light sources having different wavelengths, so two or more types of light sources may be used. There is no problem.

  The printing original plate thus obtained is attached to the surface of the plate mounting drum of the laser engraving apparatus, and the irradiated portion of the original plate is decomposed by laser irradiation according to the image to form a concave portion, whereby a printing plate is manufactured. The printing original plate obtained from the resin composition of the present invention can suppress the generation and adhesion of resin debris by using the printing original plate having a swelling ratio within a certain range, and has no printing defect and excellent resolution. A version can be provided.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

[Example 1]
(A) As component latex, NBR latex (Nippon A & L SIA-TEX NA20: gelation degree 70%, non-volatile content: non-volatile content 45%) 111 parts by mass (50 parts by mass as solid content), (B) as photopolymerizable compound , 25 parts by mass of trimethylolpropane triacrylate (molecular weight 296), 14 parts by mass of lauryl methacrylate, (C) 1.0 part by mass of benzyldimethyl ketal as a photopolymerization initiator, and PFT- manufactured by Kyoeisha Chemical as a hydrophilic polymer 3 (compound having a urethane urea structure with a molecular weight of about 20,000, nonvolatile content of 25%) 20 parts by mass, hydroquinone monomethyl ether 0.1 parts by weight as a polymerization inhibitor, and liquid butadiene rubber as a plasticizer (molecular weight about 2,000) After mixing 5 parts by mass with 5 parts by mass of toluene in a container Kneaded at 105 ° C. with a pressure kneader, followed toluene and water was removed under reduced pressure to obtain a resin composition.

[Example 2]
The component latex (A) of Example 1 was changed to NBR latex (Nippon A & L SIA-TEX NA20: gelation degree 70%, non-volatile content: non-volatile content 45%) 42 parts by mass (19 parts by mass as solid content), NBR latex (Nippon Zeon) Manufactured by SX1503A: gelation degree 0%, non-volatile content 42% non-volatile content) 74 parts by weight (31 parts by weight as solid content), except that the latex has a weight average gelation degree of 28% and Example 1 Resin compositions were obtained in the same manner.

Example 3
The component latex (A) of Example 1 was NBR latex (Nippon A &L's Siatex NA20: gelation degree 70%, non-volatile content: non-volatile content 45%) 58 parts by mass (26 parts by mass as solid content), NBR latex (Nippon Zeon) Manufactured by SX1503A: gelation degree 0%, nonvolatile content non-volatile content 42%) 57 parts by weight (24 parts by weight as solid content), except for latex having a weight average gelation degree of 36% and Example 1 Resin compositions were obtained in the same manner.

Example 4
The component latex (A) of Example 1 was NBR latex (Nippon A &L's Siatex NA20: gelation degree 70%, non-volatile content: non-volatile content 45%) 76 parts by mass (34 parts by mass as solid content), NBR latex (Nippon Zeon) Manufactured by SX1503A: gelation degree 0%, non-volatile content non-volatile content 42%) 38 parts by weight (solid content 16 parts by weight), except that the latex has a weight average gelation degree of 49% and Example 1 Resin compositions were obtained in the same manner.

Example 5
NBR latex (Nippon A &L's Siatex NA20: gelation degree 70%, non-volatile content: non-volatile content 45%) 107 parts by mass (48 parts by mass as solid content), NBR latex (Nippon Zeon) Manufactured by SX1503A: gelation degree 0%, non-volatile content non-volatile content 42%) 5 parts by mass (2 parts by mass as solid content), except for latex having a weight average gelation degree of 67% and Example 1 Resin compositions were obtained in the same manner.

Example 6
The component latex (A) of Example 1 was changed to BR latex (manufactured by Nippon Zeon, LX111NF: gelation degree 86%, nonvolatile content: nonvolatile content 55%) 78 parts by mass (43 parts by mass as solid content), NBR latex (Nippon Zeon) Product No. SX1503A: Gelation degree 0%, nonvolatile content 42% non-volatile content) 17 parts by mass (7 parts by mass as solid content), except for latex having a weight average gelation degree of 76% and Example 1 Resin compositions were obtained in the same manner.

Example 7
The component latex (A) of Example 1 was changed to BR latex (manufactured by Nippon Zeon, LX111NF: gelation degree 86%, non-volatile content 55%) 91 parts by mass (50 parts by mass as the solid content), and the weight average gelation degree A resin composition was obtained in the same manner as in Example 1 except that 86% latex was used.

Example 8
(A) component latex of Example 1 was changed to 100 parts by mass of methyl methacrylate-butadiene latex (NALSTAR MR174 manufactured by Nippon A & L: gelation degree 95%: non-volatile content 50%), and latex having a weight average gelation degree of 95% A resin composition was obtained in the same manner as in Example 1 except that.

Example 9
A resin composition was obtained in the same manner as in Example 1 except that the content 39% by mass of the photopolymerizable compound (B) in Example 1 in the photosensitive resin composition was changed to 30% by mass.

[Examples 10 and 11]
A resin composition was obtained in the same manner as in Example 1 except that the monofunctional monomer of the photopolymerizable compound (B) in Example 1 was changed to stearyl methacrylate and 2-ethylhexyl (meth) acrylate.

[Examples 12 to 14]
A resin composition was obtained in the same manner as in Example 1 except that the monofunctional monomer ratio in the photopolymerizable compound (B) of Example 1 was changed.

[Examples 15 and 16]
In Example 15, (B) the photopolymerizable compound of Example 1 was changed to trimethylolpropane trimethacrylate (molecular weight 310), and in Example 16, except that pentaerythritol triacrylate (molecular weight 298) was changed. A resin composition was obtained in the same manner as in Example 1.

[Comparative Examples 1 and 2]
In Comparative Example 1, the polyfunctional monomer in (B) the photopolymerizable compound of Example 1 was changed to a photopolymerizable oligomer (manufactured by Kyoeisha Chemical Co., Ltd., molecular weight 2700 oligobutadiene diacrylate), and in Comparative Example 2, tricyclodecane diacrylate. A resin composition was obtained in the same manner as in Example 1 except that

[Comparative Examples 3 and 4]
In Comparative Example 3, the weight average gelation degree of the latex component (A) of Example 1 was lowered to 15%, and in Comparative Example 4, Example 1 was changed except that the weight average gelation degree was changed to 0% without using latex. In the same manner, a resin composition was obtained.

[Comparative Example 5]
The content of the trimethylolpropane methacrylate used as the photopolymerizable compound in Example 1 (B) was reduced to 10%, and the photopolymerizable oligomer (Kyoeisha Chemical Co., Ltd., molecular weight 2700 oligobutadiene diacrylate) was used. A resin composition was obtained in the same manner as in Example 1 except that the combination was changed.

[Comparative Example 6]
A photopolymerizable oligomer (manufactured by Kyoeisha Chemical Co., Ltd., molecular weight 2700 oligobutadiene diacrylate) was used as a main component as the photopolymerizable compound of Example 1 except that the combination was changed to a bifunctional monomer and a monofunctional monomer. A resin composition was obtained in the same manner as in Example 1.

[Comparative Example 7]
In Comparative Example 7, except that the polyfunctional monomer in the photopolymerizable compound (B) of Example 1 was changed to an acrylate (ATMPT-9EO, molecular weight 692) of 9EO adduct of trimethylolpropane manufactured by Shin-Nakamura Chemical Co., Ltd. A resin composition was obtained in the same manner as in Example 1.

Next, creation of a printing master for laser engraving will be described.
The resin compositions obtained in Examples 1 to 16 and Comparative Examples 1 to 6 were coated with a polyester adhesive layer on a polyethylene terephthalate film having a thickness of 125 μm, and an anti-tacking layer (polyvinyl alcohol) on the same polyethylene terephthalate film. ) With a film coated (with the adhesive layer and anti-tacking layer in contact with the resin composition), and pressed with a heat press machine at 105 ° C. and a pressure of 100 kg / cm 2 for 1 minute to a thickness of 1.7 mm A sheet-like molded product was obtained. Next, this sheet-like molded product is exposed for 10 minutes on the front and back by an ultraviolet exposure machine (light source: 10R manufactured by Philips Co., Ltd.) of 8 mW / cm ² from a distance of 5 cm from the surface, and photocured to obtain a printing original plate for laser engraving. Produced.

  The printing original plates of Examples 1 to 16 and Comparative Examples 1 to 7 prepared by the above method were wound around a plate mounting drum of a laser engraving apparatus with a double-sided tape, and laser engraving was performed under the following conditions. Simultaneously with the start of laser engraving, the dust collector installed in the vicinity of the laser gun was operated, and the continuously engraved resin debris was discharged out of the apparatus. After laser engraving, the plate removed from the mounting drum was washed with water washing plate exclusive washing machine (CRS600 manufactured by Toyobo Co., Ltd., 1% washing soap aqueous solution, water temperature 40 ° C.) for 3 minutes, and adhered to the plate surface. A small amount of resin residue was removed and dried to obtain a printing plate.

As the laser engraving apparatus, a FlexPose! Direct equipped with a 300 W carbon dioxide laser manufactured by Luescher Flexo was used. The specifications of this apparatus were a laser wavelength of 10.6 μm, a beam diameter of 30 μm, a plate mounting drum diameter of 300 mm, and a processing speed of 1.5 hours / 0.5 m 2. The conditions for laser engraving are as follows. Note that (1) to (3) are conditions specific to the apparatus. Conditions can be arbitrarily set for (4) to (7), and the standard conditions of this apparatus are adopted for each condition.
(1) Resolution: 2540 dpi
(2) Laser pitch: 10 μm
(3) Drum rotation speed: 982 cm / sec (4) Top power: 9%
(5) Bottom power: 100%
(6) Shoulder width: 0.30mm
(7) Relief depth: 0.60 mm
(8) Evaluation image: 175 lpi, halftone dots in 1% increments from 1 to 100%

The following evaluation items were investigated for the obtained printing plate. The evaluation results are shown in Table 1.
(1) Adhesion degree of resin residue Using a 100 × microscope, the adhesion degree of resin residue on the printing plate surface was visually inspected and shown in the following four stages.
◎: Almost no adhesion ○: Some adhesion △: There is considerable adhesion ×: Extreme adhesion
(2) Halftone dot shape Using a 100 × microscope, a 10% halftone dot shape at 175 lpi was observed with a microscope. The shape of the halftone dot is a conical shape with no burrs or dents, and a dot top diameter of 4.0 to 4.5 μm and a depth of 0.6 mm or more is excellent in printing suitability and printing durability.
◯: Conical Δ: Partially unclear ×: Unclear (3) Halftone dot formation 175 lpi minimum halftone dot formation was measured using a 100 × microscope.
(4) Printability evaluation Ten thousand copies were printed using a flexographic printing machine, and the ink stickiness of the printed matter was visually observed. Moreover, the micro image reproducibility (175 lpi, 1 to 5% halftone dot) of the obtained printed matter was visually confirmed using a 100 × microscope. About printing durability, it visually determined using the 20 times magnifier whether the crack has generate | occur | produced in the relief after printing 10,000 copies.
Ink paste property: ○: Good △: Some color unevenness ×: Whole color unevenness Micro image printability; ○: Good △: Some dot unevenness ×: Large halftone dot unevenness
Printing durability: ○: No cracks △: Some parts ×: All parts

From the evaluation results in Table 1, it can be seen that when the specific photopolymerizable compound of the present invention is used, the weight average gelation degree of the latex is excellent as a printing plate for laser engraving in a specific range. In Comparative Examples 1 and 2, when a bifunctional monomer or a photopolymerizable oligomer is used as the photopolymerizable compound, the laser engraving property is inferior. From the results of Comparative Examples 3 to 5, it is clear that the laser engraving property is further lowered when the weight average gelation degree is low.
Moreover, although the evaluation result of the composition equivalent to description in patent document 3 of a prior art is shown in the comparative example 6, it turns out that it cannot respond to the halftone dot of 175Lpi which is finer reproducibility.
From the above results, it is clear that if the printing original plate of the present invention is used, the laser engraving performance is remarkably improved and a higher resolution printing plate is produced.

  In the flexographic printing original plate capable of laser engraving of the present invention, the resin residue generated by laser irradiation during the production of the printing plate is very rarely left attached to the plate surface. Therefore, in particular in the flexographic printing field, it can be suitably used as a printing plate for laser engraving when preparing a printing plate.

Claims (3)

  At least light-irradiate a photosensitive resin composition containing (A) a latex having a weight average gelation degree of 20% or more, (B) a photopolymerizable compound, and (C) a photopolymerization initiator to be crosslinked and cured. (B) a polyfunctional monomer having a photopolymerizable compound having three ethylenically unsaturated groups in one molecule having a molecular weight of 1,000 or less, and one ethylenically unsaturated in one molecule A flexographic printing original plate capable of laser engraving, comprising a monofunctional monomer having a group.   (B) The flexographic printing original plate capable of laser engraving according to claim 1, wherein the molecular weight of the other functional monomer in the photopolymerizable compound is 500 or less.   (B) The polyfunctional monomer of the photopolymerizable compound is one or more compounds selected from trimethylolpropane tricrelate, trimethylolpropane trimetaacrylate, or pentaerythritol triacrylate, and the monofunctional monomer is lauryl methacrylate or stearyl. The flexographic printing original plate capable of laser engraving according to claim 1 or 2, which is a methacrylate.